U.S. patent application number 15/777730 was filed with the patent office on 2019-11-07 for electric power steering apparatus.
This patent application is currently assigned to NSK LTD.. The applicant listed for this patent is NSK LTD.. Invention is credited to Takahiro TSUBAKI.
Application Number | 20190337556 15/777730 |
Document ID | / |
Family ID | 61905601 |
Filed Date | 2019-11-07 |
![](/patent/app/20190337556/US20190337556A1-20191107-D00001.png)
![](/patent/app/20190337556/US20190337556A1-20191107-D00002.png)
![](/patent/app/20190337556/US20190337556A1-20191107-D00003.png)
![](/patent/app/20190337556/US20190337556A1-20191107-D00004.png)
![](/patent/app/20190337556/US20190337556A1-20191107-D00005.png)
![](/patent/app/20190337556/US20190337556A1-20191107-D00006.png)
![](/patent/app/20190337556/US20190337556A1-20191107-D00007.png)
![](/patent/app/20190337556/US20190337556A1-20191107-D00008.png)
![](/patent/app/20190337556/US20190337556A1-20191107-D00009.png)
![](/patent/app/20190337556/US20190337556A1-20191107-D00010.png)
![](/patent/app/20190337556/US20190337556A1-20191107-D00011.png)
View All Diagrams
United States Patent
Application |
20190337556 |
Kind Code |
A1 |
TSUBAKI; Takahiro |
November 7, 2019 |
ELECTRIC POWER STEERING APPARATUS
Abstract
An electric power steering apparatus that reduces uncomfortable
feeling to a driver in steering angle control by improving
followability of an actual steering angle to a target steering
angle, and performs efficient damping to a vibration of a vehicle.
The apparatus includes a torque control section that calculates a
first motor current command value based on a steering torque and so
on, a target steering angle generating section that generates a
target steering angle based on vehicle information, and a steering
angle control section that calculates a second motor current
command value based on the target steering angle, an actual
steering angle and so on, and calculates the motor current command
value by the first and second motor current command values.
Inventors: |
TSUBAKI; Takahiro;
(Maebashi-Shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NSK LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
NSK LTD.
Tokyo
JP
|
Family ID: |
61905601 |
Appl. No.: |
15/777730 |
Filed: |
October 13, 2017 |
PCT Filed: |
October 13, 2017 |
PCT NO: |
PCT/JP2017/037145 |
371 Date: |
May 21, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B62D 15/025 20130101;
B62D 15/0285 20130101; B62D 5/0463 20130101; B62D 6/002 20130101;
B62D 5/0472 20130101; B62D 6/007 20130101 |
International
Class: |
B62D 5/04 20060101
B62D005/04; B62D 6/00 20060101 B62D006/00; B62D 15/02 20060101
B62D015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 14, 2016 |
JP |
2016-202804 |
Claims
1-13. (canceled)
14. An electric power steering apparatus that drives a motor based
on a motor current command value, and performs assist control and
steering angle control to a steering system by driving and
controlling said motor, comprising: a torque control section that
calculates a first motor current command value for said assist
control based on at least a steering torque; a target steering
angle generating section that generates a target steering angle
being a target value in said steering angle control based on
vehicle information; and a steering angle control section that
calculates a second motor current command value for said steering
angle control based on at least said target steering angle and an
actual steering angle; wherein said electric power steering
apparatus calculates said motor current command value by said first
motor current command value and said second motor current command
value; and wherein said target steering angle generating section
comprises a lateral position control section that calculates a
lateral velocity command value by a deviation between a lateral
position command value that is obtained based on said vehicle
information and a lateral position, a lateral velocity calculating
section that calculates a lateral velocity by said lateral
position, a lateral velocity control section that calculates a
basic target steering angle based on said lateral velocity command
value and said lateral velocity, and a vehicle behavior stabilizing
section that calculates a compensatory target steering angle for
damping by a lateral acceleration that is obtained based on said
vehicle information, and generates said target steering angle by
said basic target steering angle and said compensatory target
steering angle.
15. The electric power steering apparatus according to claim 14,
wherein said steering angle control section calculates said second
motor current command value in accordance with I-P control based on
a motor velocity command value that is calculated using said target
steering angle and said actual steering angle.
16. The electric power steering apparatus according to claim 14,
wherein said lateral position control section calculates said
lateral velocity command value by multiplying said deviation by a
proportional gain.
17. The electric power steering apparatus according to claim 15,
wherein said lateral position control section calculates said
lateral velocity command value by multiplying said deviation by a
proportional gain.
18. The electric power steering apparatus according to claim 14,
wherein said lateral velocity control section calculates said basic
target steering angle in accordance with I-P control using said
lateral velocity command value and said lateral velocity.
19. The electric power steering apparatus according to claim 15,
wherein said lateral velocity control section calculates said basic
target steering angle in accordance with I-P control using said
lateral velocity command value and said lateral velocity.
20. The electric power steering apparatus according to claim 14,
wherein said vehicle behavior stabilizing section comprises a phase
compensating section that performs phase compensation using a phase
compensation filter and a gain section that multiplies a gain, and
calculates said compensatory target steering angle by said lateral
acceleration through said phase compensating section and said gain
section.
21. The electric power steering apparatus according to claim 15,
wherein said vehicle behavior stabilizing section comprises a phase
compensating section that performs phase compensation using a phase
compensation filter and a gain section that multiplies a gain, and
calculates said compensatory target steering angle by said lateral
acceleration through said phase compensating section and said gain
section.
22. The electric power steering apparatus according to claim 20,
wherein a characteristic of said phase compensation filter is
changed depending on a vehicle speed.
23. The electric power steering apparatus according to claim 14,
wherein said target steering angle generating section further
comprises a first limiting section that limits said lateral
position command value by a preset first limit value.
24. The electric power steering apparatus according to claim 15,
wherein said target steering angle generating section further
comprises a first limiting section that limits said lateral
position command value by a preset first limit value.
25. The electric power steering apparatus according to claim 14,
wherein said target steering angle generating section further
comprises a rate limiting section that limits a variation of said
lateral position command value by a preset rate limit value.
26. The electric power steering apparatus according to claim 15,
wherein said target steering angle generating section further
comprises a rate limiting section that limits a variation of said
lateral position command value by a preset rate limit value.
27. The electric power steering apparatus according to claim 14,
wherein said target steering angle generating section further
comprises a lateral position command vibration eliminating section
that reduces a vibration frequency component included in said
lateral position command value for said lateral position command
value.
28. The electric power steering apparatus according to claim 15,
wherein said target steering angle generating section further
comprises a lateral position command vibration eliminating section
that reduces a vibration frequency component included in said
lateral position command value for said lateral position command
value.
29. The electric power steering apparatus according to claim 27,
wherein a characteristic that said lateral position command
vibration eliminating section has is changed depending on a vehicle
speed.
30. The electric power steering apparatus according to claim 14,
wherein said target steering angle generating section further
comprises a lateral velocity command filter section that obtains a
compensation value to improve followability of said lateral
position to said lateral position command value by said lateral
position command value using an FF filter, and compensates said
lateral velocity command value by said compensation value.
31. The electric power steering apparatus according to claim 15,
wherein said target steering angle generating section further
comprises a lateral velocity command filter section that obtains a
compensation value to improve followability of said lateral
position to said lateral position command value by said lateral
position command value using an FF filter, and compensates said
lateral velocity command value by said compensation value.
32. The electric power steering apparatus according to claim 30,
wherein a characteristic of said FF filter is changed depending on
a vehicle speed.
33. The electric power steering apparatus according to claim 14,
wherein said target steering angle generating section further
comprises a second limiting section that limits said target
steering angle by a preset second limit value.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electric power steering
apparatus that enables manual steering and automatic steering by
performing assist control and steering angle control to a steering
system by driving and controlling a motor based on a motor current
command value, and in particular to an electric power steering
apparatus that reduces an influence of vehicle vibration by
compensating a target steering angle being a target value in the
steering angle control based on vehicle information.
BACKGROUND ART
[0002] An electric power steering apparatus (EPS) which provides a
steering system of a vehicle with a steering assist torque (an
assist torque) by means of a rotational torque of a motor, applies
a driving force of the motor as the steering assist torque to a
steering shaft or a rack shaft by means of a transmission mechanism
such as gears or a belt through a reduction mechanism, and performs
assist control. In order to accurately generate the assist torque,
such a conventional electric power steering apparatus performs
feedback control of a motor current. The feedback control adjusts a
voltage supplied to the motor so that a difference between a
steering assist command value (a current command value) and a
detected motor current value becomes small, and the adjustment of
the voltage supplied to the motor is generally performed by an
adjustment of a duty ratio of pulse width modulation (PWM)
control.
[0003] A general configuration of the conventional electric power
steering apparatus will be described with reference to FIG. 1. As
shown in FIG. 1, a column shaft (a steering shaft or a handle
shaft) 2 connected to a steering wheel 1 is connected to steered
wheels 8L and 8R through reduction gears (worm gears) 3
constituting the reduction mechanism, universal joints 4a and 4b, a
rack-and-pinion mechanism 5, and tie rods 6a and 6b, further via
hub units 7a and 7b. In addition, a torsion bar is inserted into
the column shaft 2, for which a steering angle sensor 14 for
detecting a steering angle .theta. of the steering wheel 1 by means
of a twist angle of the torsion bar and a torque sensor 10 for
detecting a steering torque Tt are provided, and a motor 20 for
assisting a steering force of the steering wheel 1 is connected to
the column shaft 2 through the reduction gears 3. The electric
power is supplied to a control unit (ECU) 30 for controlling the
electric power steering apparatus from a battery 13, and an
ignition key signal is inputted into the control unit 30 through an
ignition key 11. The control unit 30 calculates a current command
value of an assist control command on the basis of the steering
torque Tt detected by the torque sensor 10 and a vehicle speed V
detected by a vehicle speed sensor 12, and controls a current
supplied to the motor 20 by means of a voltage control command
value Vref obtained by performing compensation or the like to the
current command value.
[0004] Moreover, the steering angle sensor 14 is not essential, it
does not need to be provided, and it is possible to obtain the
steering angle from a rotational angle sensor such as a resolver
connected to the motor 20.
[0005] A controller area network (CAN) 40 exchanging various
information of a vehicle is connected to the control unit 30, and
it is possible to receive the vehicle speed V from the CAN 40.
Further, it is also possible to connect a non-CAN 41 exchanging a
communication, analog/digital signals, a radio wave or the like
except with the CAN 40 to the control unit 30.
[0006] The control unit 30 mainly comprises a CPU (including an
MPU, an MCU and so on), and general functions performed by programs
within the CPU are shown in FIG. 2.
[0007] The control unit 30 will be described with reference to FIG.
2. As shown in FIG. 2, the steering torque Tt detected by the
torque sensor 10 and the vehicle speed V detected by the vehicle
speed sensor 12 (or from the CAN 40) are inputted into a current
command value calculating section 31 that calculates a current
command value Iref1. The current command value calculating section
31 calculates the current command value Iref1 that is a control
target value of a current supplied to the motor 20 on the basis of
the inputted steering torque Tt and vehicle speed V and by using an
assist map or the like. The current command value Iref1 is inputted
into a current limiting section 33 through an adding section 32A. A
current command value Irefm the maximum current of which is limited
is inputted into a subtracting section 32B, and a deviation I
(=Irefm-Im) between the current command value Irefm and a motor
current Im being fed back is calculated. The deviation I is
inputted into a proportional integral (PI) control section 35 for
improving a characteristic of the steering operation. The voltage
control command value Vref whose characteristic is improved by the
PI-control section 35 is inputted into a PWM-control section 36.
Furthermore, the motor 20 is PWM-driven through an inverter 37. The
motor current Im of the motor 20 is detected by a motor current
detector 38 and is fed back to the subtracting section 32B. The
inverter 37 is comprised of a bridge circuit of field effect
transistors (FETs) as semiconductor switching elements.
[0008] A rotational angle sensor 21 such as a resolver is connected
to the motor 20, and a rotational angle (a motor rotational angle)
Be is detected and outputted by the rotational angle sensor 21.
[0009] Further, a compensation signal CM from a compensation signal
generating section 34 is added to the adding section 32A, and a
characteristic compensation of the steering system is performed by
the addition of the compensation signal CM so as to improve a
convergence, an inertia characteristic and so on. The compensation
signal generating section 34 adds a self-aligning torque (SAT) 343
and an inertia 342 at an adding section 344, further adds the
result of addition performed at the adding section 344 with a
convergence 341 at an adding section 345, and then outputs the
result of addition performed at the adding section 345 as the
compensation signal CM.
[0010] With respect to such an electric power steering apparatus
(EPS), the EPS has been applied to a vehicle equipped with a
parking assist function by automatic steering, and further, a
proposal to apply the EPS to automatic steering in automatic
driving technique whose research and development has been recently
advanced, has been made. Such an EPS performs assist control which
a conventional EPS performs and steering angle control which
controls a steering system so that a vehicle travels in a desired
direction respectively. In the steering angle control, position and
velocity control having superior performance for responsiveness to
a target steering angle being a control target of a steering angle
and a disturbance suppression characteristic to a road surface
reaction force and so on, is used, for example, proportional (P)
control is adopted in position control, and proportional-integral
(PI) control is adopted in velocity control. Further, in order to
achieve stable automatic steering, a countermeasure to a rapid
fluctuation of the target steering angle and a vibration of a
steering wheel has been taken.
[0011] In the publication of Japanese Patent No. 3917008 B2 (Patent
Document 1), an automatic steering control apparatus is proposed
that automatically performs a steering wheel operation depending on
a set steering angle and aims at parking assist in particular. This
apparatus can switch between a torque control mode (the assist
control) and a parking assist mode (the steering angle control),
and performs the control by using prestored parking data in the
parking assist mode. Further, the apparatus performs the P-control
in the position control of the parking assist mode, and performs
the PI-control in the velocity control.
[0012] An electric power steering apparatus disclosed in Japanese
Unexamined Patent Publication No. 2013-252729 A (Patent Document 2)
performs precise steering in accordance with the target steering
angle and smooth control to rapid change of the target steering
angle by adjusting a motor current command value for automatic
control to the target steering angle depending on a vehicle speed,
and applying smoothness processing by a rate limiter to the target
steering angle. Further, the electric power steering apparatus
obtains a damping effect without a torque sensor by correcting a
current command value by means of a current command value for
damping obtained on the basis of a twist angle of a torsion
bar.
[0013] The List of Prior Art Documents Patent Documents [0014]
Patent Document 1: Japanese Patent No. 3917008 B2 [0015] Patent
Document 2: Japanese Unexamined Patent Publication No. 2013-252729
A
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0016] In the case of performing the steering angle control in a
vehicle, a disturbance and a load state are significantly changed
by a traveling vehicle speed, friction, change of a road surface
reaction force and so on, so that it is necessary to adopt a
control configuration being resistant to them. However, for
example, in the case that the road surface reaction force changes,
since a response of an actual steering angle is changed in
accordance with the change of the road surface reaction force, the
velocity PI-control which the apparatus described in Patent
Document 1 adopts is not capable of following the target steering
angle accurately, and there is a possibility that a vehicle runs
off a target track.
[0017] In order to obtain the damping effect, the apparatus
described in Patent Document 2 applies processing by such as a rate
limiter not to a process of calculating the target steering angle
but to the calculated target steering angle, so that there is a
possibility that it is difficult to perform efficient damping such
as damping processing meeting a factor of vibration.
[0018] The present invention has been developed in view of the
above-described circumstances, and an object of the present
invention is to provide an electric power steering apparatus that
reduces uncomfortable feeling to a driver in steering angle control
by improving followability of an actual steering angle to a target
steering angle, and performing efficient damping to a vibration of
a vehicle.
Means for Solving the Problems
[0019] The present invention relates to an electric power steering
apparatus that drives a motor based on a motor current command
value, and performs assist control and steering angle control to a
steering system by driving and controlling the motor, the
above-described object of the present invention is achieved by that
comprising: a torque control section that calculates a first motor
current command value for the assist control based on at least a
steering torque; a target steering angle generating section that
generates a target steering angle being a target value in the
steering angle control based on vehicle information; and a steering
angle control section that calculates a second motor current
command value for the steering angle control based on at least the
target steering angle and an actual steering angle; wherein the
electric power steering apparatus calculates the motor current
command value by the first motor current command value and the
second motor current command value; and wherein the target steering
angle generating section comprises a lateral position control
section that calculates a lateral velocity command value by a
deviation between a lateral position command value that is obtained
based on the vehicle information and a lateral position, a lateral
velocity calculating section that calculates a lateral velocity by
the lateral position, a lateral velocity control section that
calculates a basic target steering angle based on the lateral
velocity command value and the lateral velocity, and a vehicle
behavior stabilizing section that calculates a compensatory target
steering angle for damping by a lateral acceleration that is
obtained based on the vehicle information, and generates the target
steering angle by the basic target steering angle and the
compensatory target steering angle.
[0020] The above-described object of the present invention is more
effectively achieved by that wherein the steering angle control
section calculates the second motor current command value in
accordance with I-P control based on a motor velocity command value
that is calculated using the target steering angle and the actual
steering angle; or wherein the lateral position control section
calculates the lateral velocity command value by multiplying the
deviation by a proportional gain; or wherein the lateral velocity
control section calculates the basic target steering angle in
accordance with I-P control using the lateral velocity command
value and the lateral velocity; or wherein the vehicle behavior
stabilizing section comprises a phase compensating section that
performs phase compensation using a phase compensation filter and a
gain section that multiplies a gain, and calculates the
compensatory target steering angle by the lateral acceleration
through the phase compensating section and the gain section; or
wherein a characteristic of the phase compensation filter is
changed depending on a vehicle speed; or wherein the target
steering angle generating section further comprises a first
limiting section that limits the lateral position command value by
a preset first limit value; or wherein the target steering angle
generating section further comprises a rate limiting section that
limits a variation of the lateral position command value by a
preset rate limit value; or wherein the target steering angle
generating section further comprises a lateral position command
vibration eliminating section that reduces a vibration frequency
component included in the lateral position command value for the
lateral position command value; or wherein a characteristic that
the lateral position command vibration eliminating section has is
changed depending on a vehicle speed; or wherein the target
steering angle generating section further comprises a lateral
velocity command filter section that obtains a compensation value
to improve followability of the lateral position to the lateral
position command value by the lateral position command value using
an FF filter, and compensates the lateral velocity command value by
the compensation value; or wherein a characteristic of the FF
filter is changed depending on a vehicle speed; or wherein the
target steering angle generating section further comprises a second
limiting section that limits the target steering angle by a preset
second limit value.
Effects of the Invention
[0021] The electric power steering apparatus of the present
invention enables appropriate damping because it calculates the
target steering angle by applying damping processing based on the
lateral acceleration. Further the electric power steering apparatus
achieves vibration suppression of a response characteristic, and
enables improvement of followability, by performing the steering
angle control by velocity I-P control (proportional preceding type
PI control).
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] In the accompanying drawings:
[0023] FIG. 1 is a configuration diagram illustrating a general
outline of an electric power steering apparatus;
[0024] FIG. 2 is a block diagram showing a configuration example of
a control unit (ECU) of the electric power steering apparatus;
[0025] FIG. 3 is a block diagram showing a configuration example (a
first embodiment) of the present invention;
[0026] FIG. 4 is a block diagram showing a configuration example
(the first embodiment) of a target steering angle generating
section;
[0027] FIG. 5 is a block diagram showing a configuration example
(the first embodiment) of a vehicle motion control section;
[0028] FIG. 6 is a block diagram showing a configuration example of
a rate limiting section;
[0029] FIG. 7 is a graph showing an example of change of a lateral
position command value by rate limitation;
[0030] FIG. 8 is a block diagram showing a configuration example of
a lateral velocity control section;
[0031] FIG. 9 is a block diagram showing a configuration example of
a vehicle behavior stabilizing section;
[0032] FIG. 10 is a block diagram showing a configuration example
(the first embodiment) of a steering angle control section;
[0033] FIGS. 11A and 11B are Bode diagrams showing an example of a
frequency characteristic of a notch filter which a steering wheel
vibration eliminating section has, FIG. 11A shows a gain
characteristic, FIG. 11B shows a phase characteristic;
[0034] FIGS. 12A and 12B are Bode diagrams showing an example of a
frequency characteristic of a filter which a steering wheel damping
section has, FIG. 12A shows a gain characteristic, FIG. 12B shows a
phase characteristic;
[0035] FIG. 13 is a flowchart showing a whole operating example of
the present invention;
[0036] FIG. 14 is a flowchart showing an operating example (the
first embodiment) of the target steering angle generating
section;
[0037] FIG. 15 is a flowchart showing an operating example (the
first embodiment) of the steering angle control section;
[0038] FIG. 16 is a graph showing results of time responses of a
lateral position in simulations with the vehicle behavior
stabilizing section and without that;
[0039] FIG. 17 is a graph showing results of time responses of a
lateral acceleration in the simulations with the vehicle behavior
stabilizing section and without that;
[0040] FIG. 18 is a block diagram showing a configuration example
(a second embodiment) of a vehicle motion control section;
[0041] FIG. 19 is a block diagram showing a configuration example
(the second embodiment) of a target steering angle generating
section;
[0042] FIG. 20 is a block diagram showing a configuration example
(a third embodiment) of a steering angle control section; and
[0043] FIG. 21 is a flowchart showing an operating example (the
third embodiment) of the steering angle control section.
MODE FOR CARRYING OUT THE INVENTION
[0044] An electric power steering apparatus (EPS) according to the
present invention performs assist control being a function of a
conventional EPS and steering angle control necessary to automatic
steering in parking assist and automatic driving. A torque control
section and a steering angle control section operate respectively
in the assist control and the steering angle control, and the EPS
drives and controls a motor by switching motor current command
values (a first motor current command value and a second motor
current command value) outputted from respective sections. The
steering angle control calculates a motor velocity command value by
using a target steering angle and an actual steering angle,
performs I-P control (proportional preceding type PI control) on
the basis of the motor velocity command value, and calculates the
motor current command value (the second motor current command
value). Thereby, the EPS achieves vibration suppression of a
response characteristic, and becomes a control configuration
tolerant of a disturbance such as change of a road surface.
Further, the EPS calculates a lateral velocity command value by
using a lateral position and a lateral position command value being
a target value of the lateral position, and compensates a target
steering angle (a basic target steering angle) obtained by
performing the I-P control on the basis of the lateral velocity
command value by means of a target steering angle (a compensatory
target steering angle) calculated on the basis of a lateral
acceleration. Thereby, the EPS improves followability in a lateral
velocity and a damping effect to vehicle vibration in a lateral
direction.
[0045] Hereinafter, an embodiment of the present invention will be
described with reference to the accompanying drawings.
[0046] FIG. 3 shows a configuration example (a first embodiment) of
the present invention. A rotational angle sensor 21 such as a
resolver for detecting a motor rotational angle .theta.e is
connected to a motor 20, and the motor 20 is driven and controlled
through a vehicle-side-ECU (control unit) 100 and an EPS-side-ECU
200.
[0047] The vehicle-side-ECU 100 comprises a switching command
section 110 which outputs a switching command SW switching an
operation mode of the EPS on the basis of a button, a switch or the
like indicating an intention of a driver, and a target steering
angle generating section 120 which inputs a signal from a camera
(an image), a Global Positioning System (GPS) or the like and a
vehicle speed V from a vehicle speed sensor 51 as vehicle
information VI, and generates a target steering angle .theta.ref on
the basis of them. An actual steering angle .theta.r which is
detected by a steering angle sensor 52 providing for a column
shaft, is inputted into a steering angle control section 220 in the
EPS-side-ECU 200 through the vehicle-side-ECU 100. The vehicle
speed V is also inputted into the steering angle control section
120 as the vehicle information VI, and is inputted into a torque
control section 210 in the EPS-side-ECU 200 through the
vehicle-side-ECU 100. Moreover, the vehicle speed V is possible to
receive from a CAN or the like.
[0048] The operation mode of the EPS includes a "manual steering
mode" where the EPS performs the assist control and an "automatic
steering mode" where the EPS performs the steering angle control.
The switching command section 110 outputs the switching command SW
on the basis of a signal for discerning that the automatic steering
mode is entered, for example, a signal of a button or a switch
which is provided for a dashboard or in the vicinity of a steering
wheel and indicates the intention of the driver, or a signal of a
vehicle state determined in accordance with such as a parking mode
set in a shift, and the switching command SW is inputted into a
switching section 230 in the EPS-side-ECU 200.
[0049] The steering angle control section 120 generates the target
steering angle .theta.ref on the basis of the vehicle information
VI including the vehicle speed V, and the generated target steering
angle .theta.ref is inputted into the steering angle control
section 220. A detail of the steering angle control section 120
will be described later.
[0050] The EPS-side-ECU 200 comprises the torque control section
210 which calculates a motor current command value (a first motor
current command value) Itref for the assist control, the steering
angle control section 220 which calculates a motor current command
value (a second motor current command value) Imref for the steering
angle control, the switching section 230 which switches the
operation mode, a current control/driving section 240 which drives
and controls the motor 20, and a motor velocity calculating section
250 which calculates a motor velocity .omega.e. A steering torque
Tt detected by a torque sensor 53 is inputted into the torque
control section 210 and the steering angle control section 220.
[0051] The motor velocity calculating section 250 calculates the
motor velocity .omega.e on the basis of the motor rotational angle
.theta.e from the rotational angle sensor 21. The motor velocity
.omega.e is inputted into the steering angle control section
220.
[0052] The torque control section 210 comprises, for example, a
current command value calculating section 31, a compensation signal
generating section 34, an adding section 32A, and a current
limiting section 33 in a configuration example shown in FIG. 2 in
order to perform the assist control, and calculates the motor
current command value Itref corresponding to a current command
value Irefm shown in FIG. 2 by using an assist map on the basis of
the steering torque Tt and the vehicle speed V. Moreover, the
current limiting section 33 and/or the compensation signal
generating section 34 may not be comprised.
[0053] The steering angle control section 220 calculates the motor
current command value Imref on the basis of the target steering
angle .theta.ref, the actual steering angle .theta.r, the steering
torque Tt and the motor velocity .omega.e in order to perform the
steering angle control. A detail of the steering angle control
section 220 will be described later.
[0054] The switching section 230 switches between the manual
steering mode by the torque control section 210 and the automatic
steering mode by the steering angle control section 220 on the
basis of the switching command SW. The switching section 230
outputs the motor current command value Itref as the motor current
command value Iref in the manual steering mode, and outputs the
motor current command value Imref as the motor current command
value Iref in the automatic steering mode.
[0055] The current control/driving section 240 comprises, for
example, a subtracting section 32B, a PI-control section 35, a
PWM-control section 36, and an inverter 37 in the configuration
example shown in FIG. 2, and drives and controls the motor by using
the motor current command value Iref and a motor current Im which
is detected by a motor current detector 38 by an operation similar
to the configuration example shown in FIG. 2.
[0056] The target steering angle generating section 120 and the
steering angle control section 220 will be described in detail.
[0057] FIG. 4 shows a configuration example of the target steering
angle generating section 120. The target steering angle generating
section 120 comprises a vehicle state amount detecting section 130,
a target track calculating section 140, and a vehicle motion
control section 150.
[0058] The vehicle state amount detecting section 130 inputs data
outputted from the camera, the GPS, an angular velocity sensor, an
acceleration sensor and so on and the vehicle speed V from the
vehicle speed sensor 51 as the vehicle information VI, obtains a
lateral position Yp, a lateral acceleration Y.alpha. and a vehicle
state amount Cv which is necessary data for calculation at the
target track calculating section 140, and outputs them with the
vehicle speedy. The lateral position Yp is calculated as a distance
of own vehicle relative to a lane on the basis of image data of the
camera or the like and position information of the GPS. The lateral
position Yp, the lateral acceleration Y.alpha. and the vehicle
speed V are inputted into the vehicle motion control section 150.
The lateral position Yp, the lateral acceleration Y.alpha. and the
vehicle speed V can be included in the vehicle state amount Cv.
[0059] The target track calculating section 140 calculates a
lateral position command value Yref by an existing method on the
basis of the vehicle state amount Cv, and outputs it to the vehicle
motion control section 150.
[0060] The vehicle motion control section 150 calculates the target
steering angle .theta.ref on the basis of the lateral position
command value Yref, the lateral position Yp, the lateral
acceleration Y.alpha. and the vehicle speed V. FIG. 5 shows a
configuration example of the vehicle motion control section 150.
The vehicle motion control section 150 comprises a limiting section
(a first limiting section) 151, a limiting section (a second
limiting section) 158, a rate limiting section 152, a lateral
position command vibration eliminating section 153, a lateral
position control section 154, a lateral velocity calculating
section 155, a lateral velocity control section 156, a vehicle
behavior stabilizing section 157, a subtracting section 159, and an
adding section 160.
[0061] The limiting section 151 limits the lateral position command
value Yref by means of limit values (first limit values) consisting
of a preset upper limit value and lower limit value, and outputs
the limited value as a lateral position command value Yref1. This
enables limitation when an abnormal value of the lateral position
command value Yref occurs because of communication abnormality,
memory abnormality, or the like. A magnitude (an absolute value) of
the upper limit value and a magnitude of the lower limit value may
be the same or be different.
[0062] In order to avoid a sudden change of the target steering
angle caused by a rapid change of the lateral position command
value, the rate limiting section 152 limits a variation of the
lateral position command value Yref1 by setting a limit value (a
rate limit value), and outputs a lateral position command value
Yref2. This leads to improvement of safety of a driver. A
configuration example of the rate limiting section 152 is shown in
FIG. 6. A past value (data being one sample before) of the lateral
position command value Yref2 is held in a holding section
(Z.sup.-1) 164, and a difference between the past value and the
lateral position command value Yref1 which is addition-inputted
into a subtracting section 161 is calculated as a variation Yrefd1.
A variation setting section 162 limits the variation Yrefd1 by
means of preset limit values (an upper limit value and a lower
limit value), and outputs the limited value as a variation Yrefd2.
That is, when the variation Yrefd1 is within a range between the
upper limit value and the lower limit value, the variation setting
section 162 outputs the variation Yrefd1 as the variation Yrefd2 as
it is, and when the variation Yrefd1 is out of the range, the
variation setting section 162 outputs the limit value as the
variation Yrefd2. An adding section 163 adds the variation Yrefd2
to the past value of the lateral position command value Yref2 held
in the holding section (Z.sup.-1) 164, outputs the addition result
as the lateral position command value Yref2, and the lateral
position command value Yref2 is held in the holding section
(Z-.sup.1) 164. By such processing, for example, in the case that
the lateral position command value Yref1 changes by a variation
exceeding the limit value at the time point t1 as shown in FIG. 7,
the variation Yrefd1 is limited by means of the limit value at the
time point t1 and respective time points (t2 and t3) which are set
in a calculation cycle T after the time point t1 until the time
point t4 when the variation Yrefd1 does not exceed the limit value,
so that the lateral position command value Yref2 changes stepwise
as shown in FIG. 7, and matches the lateral position command value
Yref1 after the time point t4. Therefore, even if the lateral
position command value Yref1 changes rapidly, the rate limiting
section 152 can reduce the change, so that it is possible to
prevent a current from changing rapidly and reduce anxious feeling
of automatic steering to a driver.
[0063] In order to reduce an influence of a vibration phenomenon
caused by a resonance characteristic (a yaw resonance or the like)
of a vehicle in vehicle control, the lateral position command
vibration eliminating section 153 reduces a vibration frequency
component included in the lateral position command value Yref2 by
phase delay compensation or filter processing with such as a notch
filter, and outputs a lateral position command value Yref3. As the
filter, an arbitrary filter may be used if it decreases a gain in a
band of the vibration frequency and is possible to mount on the
ECU. Further, since a frequency and a gain of the yaw resonance of
a vehicle generally change depending on a vehicle speed, the phase
delay compensation and a frequency characteristic of the filter may
be changed depending on the vehicle speed. Moreover, in such as a
case where the vibration frequency component is minute, the lateral
position command vibration eliminating section 153 may be
removed.
[0064] The lateral position control section 154 calculates a
lateral velocity command value YVref by P-control of multiplying a
deviation Yd (=Yref3-Yp) between the lateral position command value
Yref3 and the lateral position Yp by a proportional gain Kypp.
[0065] The lateral velocity calculating section 155 calculates a
lateral velocity YV from the lateral position Yp. In order to
calculate it, the lateral velocity calculating section 155 can
perform a calculation equivalent to a differential, and, for
example, uses a difference calculation, a low pass filter for
eliminating a high frequency noise, and a gain. The lateral
velocity calculating section 155 uses, for example, a primary
filter as the low pass filter, and it is preferable to set a cutoff
frequency between 10 Hz and 30 Hz.
[0066] The lateral velocity control section 156 calculates a target
steering angle (a basic target steering angle) .theta.refa, by
which the lateral velocity YV follows the lateral velocity command
value YVref, by I-P control using the lateral velocity command
value YVref and the lateral velocity YV.
[0067] A configuration example of the lateral velocity control
section 156 is shown in FIG. 8. A deviation YDf (=YVref-YV) between
the lateral velocity command value YVref and the lateral velocity
YV is calculated at a subtracting section 173. The deviation YDf is
integrated and multiplied by a gain (Kyvi) at an integrating
section 171, and the result is addition-inputted into a subtracting
section 174. The lateral velocity YV is inputted also into a
proportional section 172, is multiplies by a gain (Kyvp) at the
proportional section 172, and the result is subtraction-inputted
into the subtracting section 174. The subtraction result of the
subtracting section 174 is outputted as the target steering angle
.theta.refa.
[0068] The vehicle behavior stabilizing section 157 calculates a
target steering angle (a compensatory target steering angle)
.theta.refb for more improving the damping effect to vehicle
vibration on the basis of the lateral acceleration Y.alpha.. The
vehicle behavior stabilizing section 157, for example, comprises a
phase compensating section 181 having a phase compensation filter
and a gain section 182 as shown in FIG. 9. The lateral acceleration
Y.alpha. is converted into a lateral acceleration Y.alpha.c by the
phase compensation filter at the phase compensating section 181,
the lateral acceleration Y.alpha.c is multiplied by a gain Kacc at
the gain section 182, and the multiplication result is outputted as
the target steering angle .theta.refb. The phase compensation
filter may be a primary filter or a quadratic filter, and may be
any one of a low pass filter, a high pass filter, a notch filter
and a band pass filter if it has a phase characteristic which can
be made stable. Further, it is possible to change a frequency
characteristic of the phase compensation filter depending on the
vehicle speed V so as to obtain more appropriate damping effect.
For example, a gain map corresponding to the vehicle speed V is
prepared, a cutoff frequency is changed depending on the vehicle
speed V, and the phase compensation is performed. The arrangement
of the phase compensating section 181 and the gain section 182 may
be reversed.
[0069] The target steering angle .theta.refa from the lateral
velocity control section 156 and the target steering angle
.theta.refb from the vehicle behavior stabilizing section 157 are
added at the adding section 160, and the addition result is
outputted to the limiting section 158 as a target steering angle
.theta.refc.
[0070] In order to prevent an excessive output, the limiting
section 158 limits the target steering angle .theta.refc by means
of limit values (second limit values) consisting of a preset upper
limit value and lower limit value, and outputs the target steering
angle .theta.ref.
[0071] FIG. 10 shows a configuration example of the steering angle
control section 220. The steering angle control section 220
comprises a rate limiting section 261, a steering wheel vibration
eliminating section 262, a position control section 263, a velocity
control section 264, a steering wheel damping section 269, a
limiting section 270, a subtracting section 271, and an adding
section 272.
[0072] In order to output the smoothed target steering angle
.theta.ref when the target steering angle .theta.ref changes
rapidly, the rate limit section 261 performs the rate limitation to
the target steering angle .theta.ref by a configuration and an
operation similar to the rate limiting section 152 in the vehicle
motion control section 150, and outputs a target steering angle
.theta.ref1. Because of the rate limitation of the rate limiting
section 261, for example, even if the target steering angle
.theta.ref changes as with the lateral position command value Yref1
shown in FIG. 7, the target steering angle .theta.ref1 changes
stepwise as with the lateral position command value Yref2 shown in
FIG. 7, and it is possible to reduce the rapid change.
[0073] In order to reduce an influence of vibration caused by
springiness of a torsion bar and an inertia moment of a steering
wheel in the automatic steering mode, the steering wheel vibration
eliminating section 262 reduces a vibration frequency component
included in the target steering angle .theta.ref1 by filter
processing with a notch filter, and outputs a target steering angle
.theta.ref2. A steering wheel vibration frequency by the
springiness of a torsion bar and the inertia moment of a steering
wheel (hereinafter this frequency is merely referred to a "steering
wheel vibration frequency") is about 12.5 [Hz], and the steering
wheel vibration eliminating section 262 uses the notch filter in
order to decrease only the gain in the vicinity of the steering
wheel vibration frequency, for example, 12.5.+-.5.0 [Hz]. The
steering wheel vibration eliminating section 262 uses, for example,
a filter which has a quadric transfer function G.sub.notch
expressed by the following expression 1.
G notch = .omega. d 2 .omega. n 2 s 2 + 2 .zeta. n .omega. n s +
.omega. n 2 s 2 + 2 .zeta. d .omega. d s + .omega. d 2 [ Expression
1 ] ##EQU00001##
Here, .omega.n and .omega.d are center frequencies, .zeta.n and
.zeta.d are damping constants, ands is a Laplace operator. A
frequency characteristic of the transfer function G.sub.notch in
the case of .omega.n=.omega.d=2.pi..times.12.5 [rad/s], and n=0.2
and d=0.6, is shown in FIGS. 11A and 11B. FIG. 11A shows a gain
characteristic, and FIG. 11B shows a phase characteristic. From
FIGS. 11A and 11B, it is found out that the gain is decreased at
about 12.5 Hz. The center frequencies .phi.n and .phi.d are set on
the basis of the steering wheel vibration frequency, and they are
not necessary to coincide. Since they are set in the vicinity of
the steering wheel vibration frequency, they may be set, for
example, between 2.pi..times.7.5 and 2.pi..times.17.5 [rad/s].
Further, it is possible to use a filter whose gain is decreased
more loosely than a notch filter in accordance with a range and an
amplitude of the vibration frequency component which should be
reduced, and the steering wheel vibration eliminating section 262
may be removed in such as a case where the vibration frequency
component is minute.
[0074] The position control section 263 calculates a motor velocity
command value .omega.ref by P-control of multiplying a deviation
.theta.d (=.theta.ref2-.theta.r) between the target steering angle
.theta.ref2 and the actual steering angle .theta.r by a
proportional gain Kpp.
[0075] The velocity control section 264 calculates a motor current
command value Imrefa, by which the motor velocity .omega.e follows
the motor velocity command value .omega.ref, by I-P control using
the motor velocity command value .omega.ref and the motor velocity
.omega.e. A deviation Df (=.omega.ref-.omega.e) between the motor
velocity command value .omega.ref and the motor velocity .omega.e
is calculated at a subtracting section 267. The deviation Df is
integrated and multiplied by a gain (Kvi) at an integrating section
265, and the result is addition-inputted into a subtracting section
268. The motor velocity .omega.e is inputted also into a
proportional section 266, is multiplies by a gain (Kvp) at the
proportional section 266, and the result is subtraction-inputted
into the subtracting section 268. The subtraction result of the
subtracting section 268 is outputted as the motor current command
value Imrefa. It is possible to use an actual steering angular
velocity instead of the motor velocity .omega.e, and the actual
steering angular velocity may be calculated by using the actual
steering angle .theta.r.
[0076] The steering wheel damping section 269 calculates a motor
current command value Imrefb for more improving the damping effect
to steering wheel vibration on the basis of the steering torque Tt.
The steering wheel damping section 269 calculates the motor current
command value Imrefb by phase compensation and multiplication of a
gain as with the vehicle behavior stabilizing section 157 in the
vehicle motion control section 150. A filter for the phase
compensation may be a primary filter or a quadratic filter, and may
be a low pass filter, a high pass filter or the like if it has a
phase characteristic which can be made stable. For example, an
example of a frequency characteristic in the case of using a
primary high pass filter is shown in FIGS. 12A and 12B. FIG. 12A
shows a gain characteristic, and FIG. 12B shows a phase
characteristic. Since a cutoff frequency is set on the basis of the
steering wheel vibration frequency, it is set to 12.5 Hz in FIGS.
12A and 12B. The steering wheel damping section 269 may be removed
in such as a case where the vibration frequency component which
should be reduced is minute.
[0077] The motor current command value Imrefa from the velocity
control section 264 and the motor current command value Imrefb from
the steering wheel damping section 269 are added at the adding
section 272, and the addition result is outputted as a motor
current command value Imrefc to the limiting section 270.
[0078] In order to prevent an excessive output, the limiting
section 270 limits the motor current command value Imrefc by means
of limit values consisting of a preset upper limit value and lower
limit value, and outputs the motor current command value Imref.
[0079] In such a configuration, the operating example will be
described with reference to flowcharts shown in FIGS. 13 to 15. The
operation mode of the EPS at the start of the operation is set to
the "manual steering mode".
[0080] When an operation of the steering system starts, the vehicle
speed sensor 51 and the torque sensor 53 detect the vehicle speed V
and the steering torque Tt respectively (Step S10). The torque
control section 210 in the EPS-side-ECU 200 inputs the vehicle
speed V and the steering torque Tt, and calculates the motor
current command value Itref for the assist control with the
operations similar to the current command value calculating section
31, the compensation signal generating section 34, the adding
section 32A and the current limiting section 33 shown in FIG. 2
(Step S20). The motor current command value Itref is inputted into
the current control/driving section 240 as the motor current
command value Iref through the switching section 230, and the
current control/driving section 240 drives the motor 20 by using
the motor current command value Iref (Step S30). The operations of
the steps S10 to S30 are repeated until the switching command SW is
outputted from the switching command section 110 in the
vehicle-side-ECU 100 (Step S40).
[0081] When the operation mode is changed to the "automatic
steering mode" and the switching command SW is outputted from the
switching command section 110 (Step S40), the vehicle speed V which
the vehicle speed sensor 51 detects is inputted into the target
steering angle generating section 120 as the vehicle information VI
with the signals from the camera and so on (Step S50). Further, the
actual steering angle .theta.r and the steering torque Tt which the
steering angle sensor 52 and the torque sensor 53 have detected
respectively, are inputted into the steering angle control section
220 (Step S60). Furthermore, the motor velocity calculating section
250 calculates the motor velocity .omega.e by the motor rotational
angle .theta.e from the rotational angle sensor 21, and outputs it
to the steering angle control section 220 (Step S70).
[0082] The target steering angle generating section 120 which has
inputted the vehicle information VI generates the target steering
angle .theta.ref on the basis of the vehicle information VI, and
outputs it to the steering angle control section 220 (Step S80). A
detailed operation of the target steering angle generating section
120 will be described later. The order of the operation of the
motor velocity calculating section 250 and the operation of the
target steering angle generating section 120 may be reversed, or
the operations may be performed in parallel.
[0083] The steering angle control section 220 inputs the actual
steering angle .theta.r, the steering torque Tt, the motor velocity
.omega.e and the target steering angle .theta.ref, and calculates
the motor current command value Imref for the steering angle
control on the basis of them (Step S220). A detailed operation of
the steering angle control section 220 will be described later.
[0084] After that, the switching section 230 is switched in
accordance with the switching command SW (Step S310), the motor
current command value Imref from the steering angle control section
220 is inputted into the current control/driving section 240 as the
motor current command value Iref, and the current control/driving
section 240 drives the motor 20 by using the motor current command
value Iref (Step S320). The operations of the steps S50 to S320 are
repeated until the switching command SW from the switching command
section 110 is changed (Step S330). When the switching command SW
is changed, the operation is returned to the step S10.
[0085] The detail of the operating example of the target steering
angle generating section 120 will be described with reference to a
flowchart shown in FIG. 14.
[0086] The vehicle information VI is inputted into the vehicle
state amount detecting section 130. The vehicle state amount
detecting section 130 obtains the lateral position Yp, the lateral
acceleration Y.alpha. and the vehicle state amount Cv (Step S90),
the vehicle state amount Cv is inputted into the target track
calculating section 140, and the lateral position Yp and the
lateral acceleration Y.alpha. are inputted into the vehicle motion
control section 150 with the vehicle speed V.
[0087] The target track calculating section 140 calculates the
lateral position command value Yref on the basis of the vehicle
state amount Cv (Step S100). The lateral position command value
Yref is inputted into the vehicle motion control section 150.
[0088] In the vehicle motion control section 150, the lateral
position command value Yref is inputted into the limiting section
151, the lateral position Yp is inputted into the subtracting
section 159 and the lateral velocity calculating section 155, the
lateral acceleration Y.alpha. is inputted into the vehicle behavior
stabilizing section 157, and the vehicle speed V is inputted into
the lateral position command vibration eliminating section 153 and
the vehicle behavior stabilizing section 157.
[0089] The limiting section 151 limits the lateral position command
value Yref by using the preset upper limit value and lower limit
value, and outputs the limited value as the lateral position
command value Yref1 to the rate limiting section 152 (Step S110).
That is, in the case that the lateral position command value Yref
is within the range between the upper limit value and the lower
limit value, the limiting section 151 outputs the lateral position
command value Yref as the lateral position command value Yref1 as
it is, and in the case that the lateral position command value Yref
is out of the range, the limiting section 151 outputs the upper
limit value or the lower limit value as the lateral position
command value Yref1 according to the limit value which has been
exceeded.
[0090] The rate limiting section 152 performs the rate limitation
as described above (Step S120), and outputs the lateral position
command value Yref2 to the lateral position command vibration
eliminating section 153.
[0091] The lateral position command vibration eliminating section
153 calculates the lateral position command value Yref3 obtained by
reducing the vibration frequency component included in the lateral
position command value Yref2 on the basis of the frequency
characteristic which has been set depending on the inputted vehicle
speed V (Step S130). The lateral position command value Yref3 is
addition-inputted into the subtracting section 159.
[0092] The deviation Yd is calculated by subtracting the
subtraction-inputted lateral position Yp from the lateral position
command value Yref3 (Step S140), and is inputted into the lateral
position control section 154.
[0093] The lateral position control section 154 calculates the
lateral velocity command value YVref by multiplying the deviation
Yd by the proportional gain Kypp (Step S150). The lateral velocity
command value YVref is inputted into the lateral velocity control
section 156.
[0094] The lateral velocity calculating section 155 which has
inputted the lateral position Yp calculates the lateral velocity YV
from the lateral position Yp (Step S160), and outputs it to the
lateral velocity control section 156.
[0095] The lateral velocity control section 156 calculates the
target steering angle .theta.refa in accordance with the I-P
control by using the lateral velocity command value YVref and the
lateral velocity YV (Step S170), and outputs it to the adding
section 160.
[0096] In the vehicle behavior stabilizing section 157 which has
inputted the lateral acceleration Y.alpha. and the vehicle speed V,
the phase compensating section 181 converts the lateral
acceleration Y.alpha. into the lateral acceleration Y.alpha.c by
using the phase compensation filter which has been set depending on
the inputted vehicle speed V (Step S180), the lateral acceleration
Y.alpha.c is multiplied by the gain Kacc at the gain section 182
(Step S190), and the multiplication result is outputted as the
target steering angle .theta.refb to the adding section 160.
[0097] The target steering angle .theta.refa and the target
steering angle .theta.refb are added at the adding section 160
(Step S200), and the target steering angle .theta.refc of the
addition result is inputted into the limiting section 158.
[0098] The limiting section 158 limits the target steering angle
.theta.refc with the operation similar to the limiting section 151
by using the preset upper limit value and lower limit value, and
outputs the limited value as the target steering angle .theta.ref
(Step S210).
[0099] The order of the operation to the calculation of the lateral
velocity command value YVref and the operation of the lateral
velocity calculating section 155, and the order of the operation to
the calculation of the target steering angle .theta.refa and the
operation of the vehicle behavior stabilizing section 157, may be
reversed respectively, or the operations in each pair may be
performed in parallel.
[0100] The detail of the operating example of the steering angle
control section 220 will be described with reference to a flowchart
shown in FIG. 15.
[0101] In the steering angle control section 220, the target
steering angle .theta.ref is inputted into the rate limiting
section 261, the actual steering angle .theta.r is inputted into
the subtracting section 271, the motor velocity .omega.e is
inputted into the velocity control section 264, and the steering
torque Tt is inputted into the steering wheel damping section
269.
[0102] The rate limiting section 261 performs the rate limitation
to the target steering angle .theta.ref with the operation similar
to the rate limiting section 152 in the vehicle motion control
section 150 (Step S230), and outputs the target steering angle
.theta.ref1 to the steering wheel vibration eliminating section
262.
[0103] The steering wheel vibration eliminating section 262
calculates the target steering angle .theta.ref2 by reducing the
vibration frequency component included in the target steering angle
.theta.ref1 by using the notch filter having the transfer function
G.sub.notch expressed by the expression 1 (Step S240). The target
steering angle .theta.ref2 is addition-inputted into the
subtracting section 271.
[0104] The deviation .theta.d is calculated at the subtracting
section 271 by subtracting the subtraction-inputted actual steering
angle .theta.r from the target steering angle .theta.ref2 (Step
S250). The deviation .theta.d is inputted into the position control
section 263.
[0105] The position control section 263 calculates the motor
velocity command value .omega.ref by multiplying the deviation
.theta.d by the proportional gain Kpp (Step S260). The motor
velocity command value .omega.ref is inputted into the velocity
control section 264.
[0106] The velocity control section 264 which has inputted the
motor velocity .omega.e and the motor velocity command value
.omega.ref, calculates the motor current command value Imrefa in
accordance with the I-P control by using them (Step S270), and
outputs it to the adding section 272.
[0107] The steering wheel damping section 269 which has inputted
the steering torque Tt calculates the motor current command value
Imrefb on the basis of the steering torque Tt by the phase
compensation and the multiplication of the gain (Step S280). The
motor current command value Imrefb is inputted into the adding
section 272.
[0108] The motor current command value Imrefa and the motor current
command value Imrefb are added at the adding section 272 (Step
S290), and the motor current command value Imrefc of the addition
result is inputted into the limiting section 270.
[0109] The limiting section 270 limits the motor current command
value Imrefc with the operation similar to the limiting sections
151 and 158 in the vehicle motion control section 150 by using the
preset upper limit value and lower limit value, and outputs the
limited value as the motor current command value Imref (Step
S300).
[0110] The order of the operation to the calculation of the motor
current command value Imrefa and the operation of the steering
wheel damping section 269 may be reversed, or the operations may be
performed in parallel.
[0111] Results of simulations with and without the vehicle behavior
stabilizing section 157 will be described as an effect of the
present embodiment.
[0112] The simulations use a primary phase compensation filter
where a cutoff frequency of a numerator is 1 Hz and a cutoff
frequency of a denominator is 0.2 Hz as the phase compensation
filter which the phase compensating section 181 in the vehicle
behavior stabilizing section 157 has, set the gain Kacc of the gain
section 182 so as to make the target steering angle equivalent to
50 deg to the lateral acceleration of 1 m/s.sup.2, and are
performed in the case of providing the vehicle behavior stabilizing
section 157 and in the case of not providing it. The results are
shown in FIGS. 16 and 17.
[0113] FIG. 16 sets the horizontal axis to a time [sec], sets the
vertical axis to a lateral position [m] of a vehicle, and shows
time responses of the lateral position Yp in the case of changing
the lateral position command value Yref as shown by the thin solid
line with the vehicle behavior stabilizing section 157 (the thick
solid line) and without it (the broken line). As found out from
FIG. 16, the lateral position Yp is stable without vibration in the
case of providing the vehicle behavior stabilizing section 157, on
the other hand, it is not stable with vibration in the case of not
providing the vehicle behavior stabilizing section 157.
[0114] Time responses of the lateral acceleration Y.alpha. in the
same simulations are shown in FIG. 17. FIG. 17 sets the horizontal
axis to a time [sec], sets the vertical axis to a lateral
acceleration [m/s.sup.2], and shows the lateral acceleration
Y.alpha. in the case of providing the vehicle behavior stabilizing
section 157 by the thick solid line and the lateral acceleration
Y.alpha. in the case of not providing it by the broken line as with
FIG. 16. From FIG. 17, it is found out that the lateral
acceleration Y.alpha. is hard to vibrate in the case of providing
the vehicle behavior stabilizing section 157.
[0115] Other embodiments of the present invention will be
described.
[0116] FIG. 18 shows another configuration example (a second
embodiment) of the vehicle motion control section in the target
steering angle generating section. Compared with the vehicle motion
control section 150 of the first embodiment shown in FIG. 5, a
lateral velocity command filter section 351 and an adding section
352 are added in a vehicle motion control section 350 of the second
embodiment. Other configurations are the same as those of the first
embodiment, so that the explanation is omitted.
[0117] The lateral velocity command filter section 351 has a
feedforward (FF) filter, and converts the lateral position command
value Yref2 obtained by performing the rate limitation at the rate
limiting section 152 into a lateral velocity command value (a
compensation value) YVrefc by means of the FF filter. The converted
lateral velocity command value YVrefc is added to the lateral
velocity command value YVref outputted from the lateral position
control section 154 at the adding section 352, and the addition
result is outputted as the lateral velocity command value YVrefm to
the lateral velocity control section 156. This enables improvement
of followability of the lateral position to the lateral position
command value. A phase advance filter, a high pass filter, a filter
corresponding to a differential, or the like is used as the FF
filter so as to advance a phase of the lateral position command
value Yref2. Further, it is possible to change a characteristic of
the FF filter depending on the vehicle speed V in order to more
improve the followability.
[0118] An operating example of the target steering angle generating
section in the second embodiment is shown in FIG. 19. Compared with
the operating example of that in the first embodiment shown in FIG.
14, operations of the lateral velocity command filter section 351
and the adding section 352 are added (Steps S151 and S152). The
lateral position command value Yref2 outputted from the rate
limiting section 152 is inputted into the lateral velocity command
filter section 351 in addition to the lateral position command
vibration eliminating section 153 with the vehicle speed V. The
lateral velocity command filter section 351 converts the lateral
position command value Yref2 into the lateral velocity command
value YVrefc by using the FF filter whose characteristic has been
set depending on the vehicle speed V (Step S151), and outputs the
lateral velocity command value YVrefc to the adding section 352.
The lateral velocity command value YVref outputted from the lateral
position control section 154 is inputted into the adding section
352 instead of the lateral velocity control section 156. The
lateral velocity command value YVrefc and the lateral velocity
command value YVref are added at the adding section 352 (Step
S152). The addition result is inputted into the lateral velocity
control section 156 as the lateral velocity command value YVrefm.
The order of the operation of the lateral velocity command filter
section 351, the operation from the lateral position command
vibration eliminating section 153 to the lateral position control
section 154, and the operation of the lateral velocity calculating
section 155 may be changed, or the operations may be performed in
parallel.
[0119] The configuration component (the lateral velocity command
filter section 351) having the FF filter is added to the vehicle
motion control section in the second embodiment, while it is also
possible to add a configuration component having the FF filter to
the steering angle control section.
[0120] FIG. 20 shows a configuration example (a third embodiment)
where the configuration component having the FF filter is added to
the steering angle control section. Compared with the steering
angle control section 220 in the first embodiment shown in FIG. 10,
a motor velocity command filter section 321 and an adding section
322 are added to a steering angle control section 320 in the third
embodiment. Other configurations are the same as those of the first
embodiment, so that the explanation is omitted.
[0121] The motor velocity command filter section 321 converts the
target steering angle .theta.ref1 obtained by performing the rate
limitation at the rate limiting section 261 into a motor velocity
command value .omega.refc by means of the FF filter. The converted
motor velocity command value .omega.refc is added to the motor
velocity command value .omega.ref outputted from the position
control section 263 at the adding section 322, and the addition
result is outputted as a motor velocity command value .omega.refm
to the velocity control section 264. Thereby, it is possible to
extend a control band of the actual steering angle for the target
steering angle to a high frequency side, and as a result, it is
possible to improve responsiveness of the steering angle
control.
[0122] An operating example of the steering angle control section
320 in the third embodiment is shown in FIG. 21. Compared with the
operating example of that in the first embodiment shown in FIG. 15,
operations of the motor velocity command filter section 321 and the
adding section 322 are added (Steps S261 and S262). The target
steering angle .theta.ref1 outputted from the rate limiting section
261 is inputted into the motor velocity command filter section 321
in addition to the steering wheel vibration eliminating section
262. The motor velocity command filter section 321 converts the
target steering angle .theta.ref1 into the motor velocity command
value .omega.refc by using the FF filter (Step S261), and outputs
the motor velocity command value .omega.refc to the adding section
322. The motor velocity command value .omega.ref outputted from the
position control section 263 is inputted into the adding section
322 instead of the velocity control section 264. The motor velocity
command value .omega.refc and the motor velocity command value
.omega.ref are added at the adding section 322 (Step S262). The
addition result is inputted as the motor velocity command value
.omega.refm into the velocity control section 264. The order of the
operation of the motor velocity command filter section 321 and the
operation from the steering wheel vibration eliminating section 262
to the position control section 263 may be reversed, or the
operations may be performed in parallel.
[0123] Though the switching section 230 switches the motor current
command value on the basis of the switching command SW from the
switching command section 110 in the above embodiments (the first
to the third embodiments), it is possible to gradually perform this
switching. Thereby, it is possible to reduce discontinuity of the
motor current command value in switching the operation mode.
[0124] Further, the limiting sections 151, 158 and 270, and the
rate limiting sections 152 and 261 may be removed in such a case
where a cost is more important than an effect of each section.
EXPLANATION OF REFERENCE NUMERALS
[0125] 1 steering wheel [0126] 2 column shaft (steering shaft,
handle shaft) [0127] 10, 53 torque sensor [0128] 12, 51 vehicle
speed sensor [0129] 13 battery [0130] 14, 52 steering angle sensor
[0131] 20 motor [0132] 21 rotational angle sensor [0133] 30 control
unit (ECU) [0134] 31 current command value calculating section
[0135] 33 current limiting section [0136] 34 compensation signal
generating section [0137] 35 PI-control section [0138] 36
PWM-control section [0139] 37 inverter [0140] 38 motor current
detector [0141] 100 vehicle-side-ECU [0142] 110 switching command
section [0143] 120 target steering angle generating section [0144]
130 vehicle state amount detecting section [0145] 140 target track
calculating section [0146] 150, 350 vehicle motion control section
[0147] 151, 158, 270 limiting section [0148] 152, 261 rate limiting
section [0149] 153 lateral position command vibration eliminating
section [0150] 154 lateral position control section [0151] 155
lateral velocity calculating section [0152] 156 lateral velocity
control section [0153] 157 vehicle behavior stabilizing section
[0154] 181 phase compensating section [0155] 182 gain section
[0156] 200 EPS-side-ECU [0157] 210 torque control section [0158]
220, 320 steering angle control section [0159] 230 switching
section [0160] 240 current control/driving section [0161] 250 motor
velocity calculating section [0162] 262 steering wheel vibration
eliminating section [0163] 263 position control section [0164] 264
velocity control section [0165] 269 steering wheel damping section
[0166] 321 motor velocity command filter section [0167] 351 lateral
velocity command filter section
* * * * *